1. Field of the Invention
The present invention deals with materials handling from a static receptacle and means to facilitate receptacle discharge using plural screw elements.
2. Description of the Prior Art
A live center bin is a large storage device having two end walls with two horizontal discharging screws between and at the bottom of the end walls, sloped side walls slanting towards a center lower discharge aperture and a row of vertical screws in this discharge aperture running along a line parallel to and between the two horizontal discharging screws which are also at the bottom of the vertical screws. A live center bin operates by keeping the product in the bin moving, or in quasi suspension, so that when the horizontal discharging screws require more product material for conveying out as discharging, it is available from the bottom of the moving mass above it. These screw augmented bins are utilized in handling material that will not discharge out of standard (having sloped side walls) bins which have no moving parts to augment the flow of product material towards a discharge opening. A typical product material might be cotton litters, stringy light-weight material like bagasse, small pieces of bamboo, wrote paper, shredded classified waste material, etc. These bins used on the above mentioned applications generally work, but problems arise in dealing with refuse derived fuel, hereinafter referred to as RDF. RDF is damp and contains a large amount of wire, glass, stringy rags, hoses, etc.
U.S. Pat. No. 4,432,499 teaches a portable grinder-mixer having both vertical and horizontal screws. A divider which cooperates with the screws provides cross mixing between the pair of adjacent bins effectively formed by the presence of the divider.
Generally, in bin nomenclature, when a product in a bin will discharge without having auxiliary devices in the bin, it is called mass flow. Products which will not discharge in a standard bin exhibit what is generally called plug flow. RDF is the shredded light fraction of industrial or municipal solid waste, and represents the classic example of plug flow.
The mass in live center bins is divided by the vertical screws into two separate plugs, each of which want to slide down the sloped side walls of the bin into the horizontal discharge screws.
As plug mass slides down the sloping sidewalls in the prior art bin structures, the descending end face of the descending plug of material is not in full contact with the total active surface of the two end vertical screws. As a result, the conveying action of the end vertical screws is neutralized by the loss of containment of plug material in the end vertical screw's conveying confinement. The plug material will then wedge between the end walls and the end vertical screws to form a cross-link of plug material between the separate plugs of material divided by the vertical screws in the bin. The lack of total end vertical screw surface activity caused plug material to cross-link between the end vertical screws and the end walls. Once the plugs are cross-linked by plug material wedging between the end walls and end vertical screws, the separate plugs of material in each side of the divided bin are held apart by this cross-link. Once the separate plugs are held apart, the plug material then begins to bridge by forming an arc of plug material in the cornering space formed upon the sloping side walls above the horizontal screws and the row of vertical screws. An arc of bridging plug material may form along the entire length in the bottom cornering space formed by the row of vertical screws and the adjacent sloped bin side wall above the horizontal screws.
When either of the masses forming the separate plugs in a bin cannot flow into the horizontal and or the vertical screws, there is in effect a solid cross-linking of the mass between the two plugs. This cross-linking will hold the two plugs apart as well as hold them up so that the plug material cannot slide into either the vertical or the horizontal screws. The resulting binding friction of the plug material will be enough to keep the plug material in an arcing bridge and cross-link to prevent it from moving into the screws augmenting discharge.